Cellular and Molecular Mechanisms of Corneal Inflammation and Wound
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Cellular and Molecular Mechanisms of Corneal Inflammation and Wound Healing By Debjani Gagen, BA Biology DISSERTATION In partial fulfillment of requirements of the degree of DOCTOR OF PHILOSOHPY in PHYSIOLOGICAL OPTICS Presented to the Graduate faculty of the College of Optometry University of Houston August, 2011 DEDICATION This dissertation is dedicated to my mother, the late Dipika DasGupta, my father, Ramlal DasGupta, and my sister, Roni DasGupta. Thank you all for everything you have sacrificed for me. I owe my current and future success to your unconditional love and unwavering support. ACKNOWLEDGEMENTS I would like to begin by thanking my advisor, Dr. Alan Burns, for his continuous support, guidance, and encouragement over the last 10 years. I could not have come this far without his remarkable patience and outstanding teaching skills. Dr. Burns, it was a genuine honor to work with you and words can not express my gratitude to for taking me under your wing and being such an extraordinary advisor and friend. I would also like to express my deepest appreciation to my committee members Dr. Rolando Rumbaut, Dr. Alison McDermott, and Dr. William Miller. To Dr. Rumbaut, thank you for your help and support throughout my time at Baylor and for excellent guidance and encouragement during my time as a graduate student at University of Houston College of Optometry. To Dr. Alison McDermott, thank you for motivating me to strive for excellence and being a wonderful role model for female scientists. To Dr. William Miller, thank you for taking the time to participate in my committee and you’re your encouragement. I would like to also thank Dr. Laura Frishman, for all her dedication to individual student success and to the graduate program at UHCO. Dr. Frishman, you are the foundation of the program I respect you immensely for the time and effort you put towards your students. I would also like to thank Dr. C.Wayne Smith, without whom I would have never had the opportunity to work in a laboratory. Dr. Smith, you opened the door for my future and I will always be grateful for your kindness, encouragement, and friendship. I would like to thank and acknowledge the hard work, dedication, and constant support of Mrs. Evelyn Brown. Evelyn, you will always be my “lab mom”. Finally, I would like to thank the staff and students at UHCO and Baylor College of Medicine, Section of Leukocyte Biology, for their support and friendship. DISSERTATION ABSTRACT Purpose: Accidental or surgical-induced trauma (e.g., refractive surgery) to the corneal epithelium results in keratocyte death immediately below the wound. Subsequent recovery of keratocytes during healing often remains incomplete, even after many years. Keratocytes produce essential proteins that help maintain corneal stability and preserve corneal clarity, and incomplete keratocyte repopulation after injury can result in loss of normal corneal structure (e.g., keratectasia) and impaired vision. To date, very little is known about the mechanisms regulating keratocyte repopulation. In the mouse, central corneal epithelial abrasion not only evokes keratocyte death, but also neutrophil (PMN), platelet, and γδ T cell recruitment out of the limbal vessels and into the stroma. This inflammatory cell recruitment is necessary for efficient epithelial cell and epithelial nerve recovery. CD18, ICAM-1, and P-selectin are adhesion molecules linked to the regulated recruitment of these inflammatory cells. The purpose of this Dissertation is to determine if the molecular mechanisms regulating inflammatory cell recruitment into the injured cornea are necessary for keratocyte repopulation following central epithelial abrasion. Methods: A 2 mm diameter central epithelial region was mechanically debrided from corneas of male wild type C57Bl/6 (WT), CD18 mutant (hypomorphic), ICAM-1-/-, TCRδ-/- (deficient in γδ T cells) and P-selectin-/-mice. Injured and uninjured corneas were prepared for transmission electron microscopy or immunofluorescence microscopy. PMN-keratocyte interactions, total PMN infiltration (per mm2), total and extravascular (EV) platelet accumulation (per mm2), and keratocyte repopulation were morphometrically analyzed using stereological methods. In vitro analyses, using cultured mouse keratocytes and extravasated PMNs, were performed to investigate PMN motility on keratocytes. Results: Previously, it was determined that PMN CD18 mediated close surface contacts between the PMN and keratocyte. The current studies show keratocyte ICAM- 1, a ligand for CD18, also mediates PMN-keratocyte surface contact, and contacts were significantly reduced in ICAM-1-/- mice compared to WT (21.5 ± 3.0% versus 39.9 ± 3.5%, respectively), consistent with the idea that ICAM-1 binds to PMN CD18 to mediate the cell-cell close surface contact. Antibody blockade of PMN CD18 or keratocyte ICAM-1 markedly reduced PMN motility on keratocytes, in vitro (by 33% and 47.5%, respectively), suggesting CD18 and ICAM-1 play a functional role in promoting PMN migration on keratocytes. PMN and platelet recruitment were greatest in ICAM-1-/- mice and, 4 days after corneal abrasion, anterior central (AC) keratocyte numbers returned to baseline, demonstrating ICAM-1 negatively regulates PMN infiltration and platelet accumulation. AC keratocyte repopulation in WT and CD18 mutant mice was significantly lower than their respective baseline counts (by 28% and 56%, respectively). There were no differences in PMN infiltration between WT and CD18 mutant mice but platelet accumulation was blunted in CD18 mutant mice, suggesting platelets, not PMNs, participate in keratocyte recovery. Previous studies show platelet P-selectin and γδ T cells are required for efficient epithelial healing. AC keratocyte repopulation in P-selectin- /- and TCRδ-/- mice only recovered to 31% and 23% of their baselines, respectively. However, infusion of WT platelets into P-selectin-/- mice “rescued” keratocyte repopulation, bringing it back to P-selectin baseline values. Additionally, AC keratocyte repopulation in platelet-depleted WT mice recovered to only 29% of WT baseline. Conclusion: Collectively, these data confirm platelet recruitment is necessary for efficient keratocyte recovery. Interestingly, EV platelet recruitment in TCRδ-/- mice was greater than WT (by 62%) although keratocyte repopulation was low; however, EV platelets in TCRδ-/- mice showed less evidence of shape change, suggesting they were less“activated” in the absence of γδ T cells. The evidence provided in this Dissertation demonstrates a role for adhesion molecules and inflammatory cells in mediating PMN- keratocyte interactions, facilitating PMN migration, regulating inflammatory cell recruitment, and promoting keratocyte repopulation following corneal epithelial abrasion. Collectively, the data suggest this inflammatory cascade is necessary for keratocyte recovery during wound healing. TABLE OF CONTENTS LIST OF TABLES………………………………………………………………..…………..................vi LIST OF FIGURES AND LEGENDS………………………………………………………...............vii APPENDIX FIGURE LIST…………………………………………………………...............……..….ix ABBREVIATIONS.........................................................................................................................x THE NEED FOR NEW TREATMENT OPTIONS TO PROMOTE CORNEAL WOUND HEALING: AN OVERVIEW ....................................................................................................... 1 CHAPTER 1: INTRODUCTION .................................................................................................. 5 1.1 OVERVIEW OF THE CORNEA ....................................................................................... 5 1.1.1 Corneal Morphogenesis ....................................................................................... 5 1.1.2 Corneal Anatomy and Physiology ......................................................................... 6 1.1.2.1 Corneal Layers .................................................................................................. 6 1.1.2.2 Corneal Innervation ........................................................................................... 7 1.1.2.3 Corneal Collagen ............................................................................................... 8 1.1.2.4 Keratocytes ........................................................................................................ 9 1.1.3 General Paradigm of Inflammation ..................................................................... 10 1.1.3.1 Immune Cells ................................................................................................... 12 1.1.3.1.1 Neutrophils ................................................................................................. 13 1.1.3.1.2 Platelets ...................................................................................................... 15 1.1.3.1.3 γδ T-cells .................................................................................................... 17 1.1.3.2 Adhesion Molecules That Facilitate Immune Cell Infiltration............................. 18 1.1.3.2.1 CD18 .......................................................................................................... 18 1.1.3.2.2 ICAM-1 ....................................................................................................... 20 1.1.3.2.3 P-selectin .................................................................................................... 21 1.2 CORNEAL INFLAMMATION AND HEALING .............................................................